In recent years, a flexible device has been developed; in the flexible device, a semiconductor element, a light-emitting element, and the like are provided over a flexible substrate. Typical examples of the flexible device include, as well as a lighting device and an image display device, a variety of semiconductor circuits including a semiconductor element such as a transistor.
As a method of manufacturing a semiconductor device including a flexible substrate, the following technique has been developed: a semiconductor element such as a thin film transistor (TFT) is formed over a support substrate (e.g., a glass substrate or a quartz substrate), and then the semiconductor element is transferred to a flexible substrate. This technique needs a step of separating a layer including the semiconductor element from the support substrate.
For example, Patent Document 1 discloses a separating technique using laser ablation as follows. A separation layer formed of amorphous silicon or the like is formed over a substrate, a layer to be separated is formed over the separation layer, and the layer to be separated is bonded to a transfer body with a bonding layer. The separation layer is ablated by laser irradiation, so that peeling occurs in the separation layer.
Patent Document 2 discloses a separating technique as follows. A metal layer is formed between a substrate and an oxide layer and peeling is performed at the interface between the oxide layer and the metal layer by utilizing weak bonding at the interface, so that a layer to be separated and the substrate are separated from each other.